Deinking of waste paper



United States Patent 3,354,027 .DEINKHNG 0F WASTE PAPER Shati Ul Hossain and Antal Anthony Pataki, Sault Ste. Marie, Ontario, Canada, assignors to Abitibi Power & Paper Company, Limited, Sault Ste. Marie, Ontario, Canada, a corporation of Canada No Drawing. Filed Dec. 9, 1963, Ser. No. 329,210 Claims priority, application Canada, Sept. 11, 1963,

3 Claims. (Cl. 1625) ABSTRACT OF THE DISCLOSURE A process for deinking waste paper in which the waste paper is treated with an alkaline chemical agent such as sodium sulp'hite and a polymer whose repeating units possess the structure of a lactam or a substituted lactam such as polyvinyl pyrrolidone.

This invention relates to a process for deinking waste paper. One of the main problems in the reuse of waste paper such as newsprint is that of deinking the waste .paper. Newspapers usually contain 1 to 2% of printing ink consisting largely of carbon black, petroleum oils and a suitable dye solution. The deinking operation may be divided into two stages, the first being the cooking or defibrating stage in which the ink particles are loosened frornthe fibre surface. Thesecond stage is the ink re moval stage in which the released ink particles are physically separated from the fibre slurry. This invention is particularly concerned with the first stage, that is to say, the cooking stage.

. In,0ur prior Canadian application No. 863,968 filed Dec. 7, 1962, it was explained that various alkalies had been used as thechemical agent in the cooking stage, including sodium hydroxide, sodium carbonate, sodium f silicate and it was proposed that deinking be carried out instead with an alkali'metal sulphite, preferably sodium sulphite.

Ithas now been foundthat improved results can be obtained by deinking with an alkaline chemical agent and a soluble polymer of the type described below. Although it is preferred that the alkaline chemical agent be sodium sulphite, other soluble alkaline chemical agents including sodium bisulphite, sodium tripolyphosphate, sodium pyrophosphate, sodium metasilicate, sodium hydroxide, sodiuni carbonate and sodium silicate can be used as the soluble alkaline chemical agent.

The term soluble polymer? may be defined as a sub-- stance of high molecular weight which forms a solution or a dispersion in aqueous media approaching, in general,

the characteristics of aqueous colloidal dispersions. The particular soluble polymers used in accordance with this invention are polyampholytes, and polymers-whose repeating unitspossessthe structureof a lactam or a substituted-lactam. Polyampholytes may be defined as macromolecular substances, which in solution, contain both positive and negative charges in their molecular structure. The net charge on a polyampholyte macromolecule is usually governed by .the pH of the medium of dispersion. Soluble proteins, as a class, are typical examples of poly- 'empholytes'y a 3,354,627 Patented Nov. 21, 1957 ing a soluble alkaline deinking agent and a soluble polymer selected from the group consisting of polyampholytes such as proteins, and polymers having a lactam or a substituted lactam structure.

In the experiments described in the examples, the pulping action was accomplished in a pulper sold under the trade name Turboflex. The waste paper was the Milwaukee Sentinel or the Toronto Star. The brightness of the reslushed unprinted sections of Milwaukee Sentinel was 57 and that of the reslushed printed sections 48. The experiments were conducted with 2.5 lb., 5 lb. and 7.5 lb. of paper depending on the consistency during pulping (2%, 4% and 6%, respectively). No attempt was made to discard sections printed with coloured inks, and their proportion in the furnish to the pulper, in general, closely corresponded to that in the original newspapers.

The newspaper sheets were torn into quarters by hand and placed in the pulper. The requisite quantities of the chemicals and water were then added, the temperature of the water being adjusted to a predetermined level, usually around 60 C. The pulping was carried out for a specified length of time, usually 10 min. Samples were then withdrawn in -g. (on a moisture-free basis) batches and floated for approximately 10 min. in a laboratory-model Denver flotation cell. (The cell used was characterized by the manufacturer as a laboratory-model Sub A flotation machine) The consistency during fio tation was adjusted to approximately 1%. After flotation, the pulp slurry was drained, the fibre mat collected and its brightness determined on sheets made in accordance with standard T.A.P.P.I. procedure. The brightness readings were taken with an Elrepho brightness instrument at 457 mmu. (millimicrons) wavelength and reported to the nearest integer. In addition, reflectance measurements were often taken over the range 426 mmu. to 681 mmu. to establish the colour reflectance curve for the pulp.

The pulping was conducted with various alkalies such as sodium sulphite, sodium tripolyphosphate, sodium pyrophosphate and sodium metasilicate, in different amounts; the soluble polymers used included polyvinyl pyrrolidone, animal blood, casein, animal glue and Protein Colloid lV. The amounts of the latter were varied between 0.2%, and 1.0%, based on the weight of the waste paper. In certain experiments, the polymer was mixed with surfactants such as soap or Triton X- (a nonionic alkyl aryl polyether alcohol) and chelating agents such as Versenex-SO. (The pentasodium salt of .diethylenetriamine penta-acetic acid.) In each case the 'after kneading for a minute or two for proper mixing,

placed in a heating bath at 60 C. for 1 hour.

Example The results obtained following the foregoing procedure are set forth below in Table I in which TPP is an abbreviation for sodium tripolyphosphate; PVP is an abbreviation for polyvinyl pyrrolidone, metso refers to sodium metasilicate, and Protein Colloid 1-V is basically a collagen based protein manufactured by extracting collagen and refining to ensure a uniform product. The molecular weight was about 10,000 and the isoelectric pH in the neighbourhood of 5. This particular product-Protein Colloid l-V-was manufactured by Swift & Company, Chicago, Ill., U.S.A.

rnent showed that the deinking technique with soluble polymers, as embodied in the present invention was effective with waste paper stored under extremely adverse weather conditions.

Colour curves were obtained and it appeared from these that the unbleached deinked pulps had higher reflectance values than the unprinted sections in the blue and part of the green region of the spectrum. It thus ap- TABLE I Consistency No. Type of Paper Chemical System during Brightness Pulping 1..." Milwaukee Sentinel- 3% NazSO plus 0.5% 'IPP plus 1.0% PVP K-30 2 58 2 do 3% Na SO; plus 0.5% TPP plus 0.5% casein 2 58 3% Na SO plus 0.5% TPP plus 1.0% animal glue 4 57 3% NazSO plus 0.5% TPP plus 0.2% Protein Colloid l-V 2 57 3% Na SOQ plus 0.5% TPP plus 0.5% Protein Colloid 1V 2 59 1% Na SO plus 0.5% TPP plus 0.5% Protein Colloid 1V 2 57 3% NazSOQ plus 0.5% TPP plus 0.5% Protein Colloid 1-V 2 58 5% NazSOs plus 0.5% TPPplus 0.5% Protein Colloid 1V 2 53 NazSOs plus 0.5% TPP plus 0.5% Protein Colloid 1-V... 2 59 3% NazSO plus 1% TPP plus 1.0% Protein Colloid 1-V 4 5g 3% Na SO plus 0.2% TPP plus 0.1% Triton X- 0 plus 0.5% Prot n 00110 4 58 3% Na SOz plus 0.5% Protein Colloid 1-V 2 57 3% NazSO; plus 0.2% VerseneX-80 plus 0.5% Protein Colloid 1-V 2 59 1% TPP plus 0.5% Protein Colloid 1-V. 2 56 1.5% TPP plus 0.5% Protein Colloid 1-V 2 56 1% NarPzO plus 0.5% Protein Colloid 1-V 2 56 0.2% METSO plus 0.5% Versenex-SO plus 0.5% Protein Colloid 1V 2 55 3% NazSO; plus 0.5% TPP plus 1% soap plus 0.2% Protein Colloid 1-V 2 60 3% Na SO3 plus 0.5% TPP plus 1% soap plus 0.2% PVP K-30 2 58 3% Na SO plus 0.5% TPP plus 1% soap plus 0.2% casein 2 59 3% gazsos plus 0.5% TPP plus 0.5% Protein Colloid 1V g 27 0. 1 6 {(a) 3% Na SOQ plus 0.5% TPP plus 0.5% Protein Colloid 1-V 2 (a) 58 (b) Bleached (after floating) with 0.2% N a S04 plus 0.5% TPP- 4 (b) 61 24-." Toronto Star a 3% lam-2S0; plus 0.5% TPP plus 0.5% Protein Colloid 1-V 2 25-.- 0. o 26. Milwaukee Sentinel. .do 2 58 1 Protein Colloid added in the flotation cell.

2 Pulped at a temp. between 6-10 C. for mm. 3 Less than a week old.

4 12 months old.

It will be noted from the experiments set forth in the above example that soluble polymers of the type disclosed were effective deinking agents when used with a suitable alkali system. The most suitable alkali, system was found to be a combination of sodium sulphite with a small amount of sodium tripolyphos-phate. When this alkali system was used with Protein Colloid 1-V( Experiments Nos. 4-10) the brightness of the deinked pulps were actually 1 to 2 points higher than that of the corresponding unprinted edge sections. Experiment No. was on a newspaper which had been aged for twelve months. The brightness of the unprinted edge sections of this paper had fallen to 55 but the deinked brightness was 56. This shows that a deinking system in accordance with this ,invention can successfully be used for deinking waste paper aged for a considerable period of time.

It is apparent that the amount of sodium sulphite or other alkaline deinking agent may be widely varied. Quantities in the range of l to 10% can be used but the preferred range is between 3 and 5%. Surfactants such as soap or chelating agents such as the pentasodium salt of diethylenetriarnine penta-acetic acid are compatible with soluble polymers such as proteins or polyvinyl pyrrolidone. It will also be noted that the addition of the soluble polymers, may, as demonstrated .in Experiment 21, be added at points other than the pulper, such as in the flotation .cell. It was furthermore shown that the pulping temperature may be widely varied. Experiment No. 22 was performed with the water temperature at 6 C. at the beginning of pulping.

Experiment No. 26 was conducted on waste paper which was stored outside during the winter months (with temperatures often dropping below 0 F.). This experipeared that the deinking treatment in accordance with the invention enhanced the reflectance in the blue region at the expense of the reflectance in the yellow-red region, conferring on the deinked pulp a pleasing blue-white shade rather than merely restoring the yellow-white of the original stock.

We claim:

1. In a process for deinking waste paper the step of treating the waste paper in a solution containing a soluble alkaline deinking agent and polyvinyl pyrrolidone.

2. A process as in claim 1 in which the soluble alkaline deinking agent is sodium sulphite.

3. A process as in claim 2 in which the polyvinyl pyrrolidone is in the amountof 0.2 to 1% based on the weight of waste paper.

. References Cited UNITED OTHER REFERENCES West: Deinking of Paper, pp. 5 to 11, pub. by Institute of Paper Chemistry, Appleton, Wis., April 1943.

DONALL H. SYLVESTER, Primary Examiner.

HOWARD R. CAINE, Examiner. 

1. IN A PROCESS FOR DEINKING WASTE PAPER THE STEP OF TREATING THE WASTE PAPER IN A SOLUTION CONTAINING A SOLUBLE ALKALINE DEINKING AGENT AND POLYVINYL PYRROLIDONE. 